[RN] Move setting last N action to base/conference

This is in preparation for an upcoming "audio only mode" feature. Setting last N
will also be required for it, so this patch factors out the action and makes it
public so other modules can reuse it.

In addition, if the value is set to undefined the configured default value (or
-1 if absent) is picked.

react/features/base/conference/actionTypes.js

  */
 export const LOCK_STATE_CHANGED = Symbol('LOCK_STATE_CHANGED');
 
+/**
+ * The type of redux action which sets the video channel's lastN (value).
+ *
+ * {
+ *     type: SET_LASTN,
+ *     lastN: number
+ * }
+ *
+ */
+export const SET_LASTN = Symbol('SET_LASTN');
+
 /**
  * The type of the Redux action which sets the password to join or lock a
  * specific JitsiConference.

react/features/base/conference/actions.js

     CONFERENCE_WILL_JOIN,
     CONFERENCE_WILL_LEAVE,
     LOCK_STATE_CHANGED,
+    SET_LASTN,
     SET_PASSWORD,
     SET_ROOM
 } from './actionTypes';
 } from './constants';
 import { _addLocalTracksToConference } from './functions';
 
+import type { Dispatch } from 'redux';
+
 /**
  * Adds conference (event) listeners.
  *
     };
 }
 
+/**
+ * Sets the video channel's last N (value) of the current conference. A value of
+ * undefined shall be used to reset it to the default value.
+ *
+ * @param {(number|undefined)} lastN - The last N value to be set.
+ * @returns {Function}
+ */
+export function setLastN(lastN: ?number) {
+    return (dispatch: Dispatch<*>, getState: Function) => {
+        if (typeof lastN === 'undefined') {
+            const { config } = getState()['features/base/lib-jitsi-meet'];
+
+            /* eslint-disable no-param-reassign */
+
+            lastN = config.channelLastN;
+            if (typeof lastN === 'undefined') {
+                lastN = -1;
+            }
+
+            /* eslint-enable no-param-reassign */
+        }
+
+        dispatch({
+            type: SET_LASTN,
+            lastN
+        });
+    };
+}
+
 /**
  * Sets the password to join or lock a specific JitsiConference.
  *

react/features/base/conference/middleware.js

 import { TRACK_ADDED, TRACK_REMOVED } from '../tracks';
 
 import { createConference } from './actions';
+import { SET_LASTN } from './actionTypes';
 import {
     _addLocalTracksToConference,
     _handleParticipantError,
     case PIN_PARTICIPANT:
         return _pinParticipant(store, next, action);
 
+    case SET_LASTN:
+        return _setLastN(store, next, action);
+
     case TRACK_ADDED:
     case TRACK_REMOVED:
         return _trackAddedOrRemoved(store, next, action);
     return next(action);
 }
 
+/**
+ * Sets the last N (value) of the video channel in the conference.
+ *
+ * @param {Store} store - The Redux store in which the specified action is being
+ * dispatched.
+ * @param {Dispatch} next - The Redux dispatch function to dispatch the
+ * specified action to the specified store.
+ * @param {Action} action - The Redux action SET_LASTN which is being dispatched
+ * in the specified store.
+ * @private
+ * @returns {Object} The new state that is the result of the reduction of the
+ * specified action.
+ */
+function _setLastN(store, next, action) {
+    const { conference } = store.getState()['features/base/conference'];
+
+    if (conference) {
+        try {
+            conference.setLastN(action.lastN);
+        } catch (err) {
+            console.error(`Failed to set lastN: ${err}`);
+        }
+    }
+
+    return next(action);
+}
+
 /**
  * Synchronizes local tracks from state with local tracks in JitsiConference
  * instance.

react/features/mobile/background/actionTypes.js

  * The type of redux action to set the AppState API change event listener.
  *
  * {
- *      type: _SET_APP_STATE_LISTENER,
- *      listener: Function
+ *     type: _SET_APP_STATE_LISTENER,
+ *     listener: Function
  * }
  *
  * @protected
  * app is going to the background.
  *
  * {
- *      type: _SET_BACKGROUND_VIDEO_MUTED,
- *      muted: boolean
+ *     type: _SET_BACKGROUND_VIDEO_MUTED,
+ *     muted: boolean
  * }
  *
  * @protected
 export const _SET_BACKGROUND_VIDEO_MUTED
     = Symbol('_SET_BACKGROUND_VIDEO_MUTED');
 
-/**
- * The type of redux action which sets the video channel's lastN (value).
- *
- * {
- *      type: _SET_LASTN,
- *      lastN: boolean
- * }
- *
- * @protected
- */
-export const _SET_LASTN = Symbol('_SET_LASTN');
-
 /**
  * The type of redux action which signals that the app state has changed (in
  * terms of execution mode). The app state can be one of 'active', 'inactive',
  * or 'background'.
  *
  * {
- *      type: APP_STATE_CHANGED,
- *      appState: string
+ *     type: APP_STATE_CHANGED,
+ *     appState: string
  * }
  *
  * @public

react/features/mobile/background/actions.js

+import { setLastN } from '../../base/conference';
 import { setVideoMuted } from '../../base/media';
 
 import {
     _SET_APP_STATE_LISTENER,
     _SET_BACKGROUND_VIDEO_MUTED,
-    _SET_LASTN,
     APP_STATE_CHANGED
 } from './actionTypes';
 
  */
 export function _setBackgroundVideoMuted(muted: boolean) {
     return (dispatch, getState) => {
-        // Disable remote video when we mute by setting lastN to 0.
-        // Skip it if the conference is in audio only mode, as it's
-        // already configured to have no video.
+        // Disable remote video when we mute by setting lastN to 0. Skip it if
+        // the conference is in audio-only mode, as it's already configured to
+        // have no video. Leave it as undefined when unmuting, the default value
+        // for last N will be chosen automatically.
         const { audioOnly } = getState()['features/base/conference'];
 
         if (!audioOnly) {
-            let lastN;
-
-            if (muted) {
-                lastN = 0;
-            } else {
-                const { config } = getState()['features/base/lib-jitsi-meet'];
-
-                lastN = config.channelLastN;
-                if (typeof lastN === 'undefined') {
-                    lastN = -1;
-                }
-            }
-
-            dispatch({
-                type: _SET_LASTN,
-                lastN
-            });
+            dispatch(setLastN(muted ? 0 : undefined));
         }
 
         if (muted) {

react/features/mobile/background/middleware.js

 } from './actions';
 import {
     _SET_APP_STATE_LISTENER,
-    _SET_LASTN,
     APP_STATE_CHANGED
 } from './actionTypes';
 
         break;
     }
 
-    case _SET_LASTN: {
-        const { conference } = store.getState()['features/base/conference'];
-
-        if (conference) {
-            try {
-                conference.setLastN(action.lastN);
-            } catch (err) {
-                console.warn(`Failed to set lastN: ${err}`);
-            }
-        }
-
-        break;
-    }
-
     case APP_STATE_CHANGED:
         _appStateChanged(store.dispatch, action.appState);
         break;